relax version pins in setup.py for non-Py2 users

setup.py

@@ -8,6 +8,8 @@ import setuptools
 from setuptools import setup, find_packages
 import sys
 
+PY2 = sys.version_info[0] == 2
+
 # Borrowed from pip at https://github.com/pypa/pip/blob/62c27dee45625e1b63d1e023b0656310f276e050/setup.py#L11-L15
 here = os.path.abspath(os.path.dirname(__file__))
 
@@ -28,8 +30,6 @@ def get_version():
 
 
 install_requires = [
-    "setuptools==44.0.0",
-    "Jinja2<3.0.0,>=2.10.1",
     "boto>=2.36.0",
     "boto3>=1.9.201",
     "botocore>=1.12.201",
@@ -42,18 +42,40 @@ install_requires = [
     "pytz",
     "python-dateutil<3.0.0,>=2.1",
     "python-jose<4.0.0",
-    "mock<=3.0.5",
     "docker>=2.5.1",
     "jsondiff>=1.1.2",
     "aws-xray-sdk!=0.96,>=0.93",
     "responses>=0.9.0",
     "idna<3,>=2.5",
     "cfn-lint>=0.4.0",
-    "sshpubkeys>=3.1.0,<4.0",
-    "zipp==0.6.0",
-    "more-itertools==5.0.0"
 ]
 
+#
+# Avoid pins where they are not necessary.  These pins were introduced by the
+# following commit for Py2 compatibility.  They are not required for non-Py2
+# users.
+#
+#   https://github.com/mpenkov/moto/commit/00134d2df37bb4dcd5f447ef951d383bfec0903c
+#
+if PY2:
+    install_requires += [
+        "Jinja2<3.0.0,>=2.10.1",
+        "mock<=3.0.5",
+        "more-itertools==5.0.0",
+        "setuptools==44.0.0",
+        "sshpubkeys>=3.1.0,<4.0",
+        "zipp==0.6.0",
+    ]
+else:
+    install_requires += [
+        "Jinja2>=2.10.1",
+        "mock",
+        "more-itertools",
+        "setuptools",
+        "sshpubkeys>=3.1.0",
+        "zipp",
+    ]
+
 extras_require = {
     'server': ['flask'],
 }